CHICAGO -- At least 70 percent of all new drugs introduced in the United States in the past 25 years come from nature despite the use of sophisticated techniques to design products in the lab, researchers reported Monday.

Their study indicates that a back-to-nature approach might yield better possibilities for companies looking for the next blockbuster drug.

Drug discovery hit a 24-year low in 2004, with just 25 unique compounds known as new chemical entities introduced that year, said David Newman, who runs the U.S. National Cancer Institute's natural products branch.

"Chemists started making libraries of hundreds of thousands to millions of compounds. But they were simple compounds," he said in a telephone interview.

Newman links a dearth of new drug development at U.S. drug companies with the shift away from nature as a main source of drug compounds.

"Wyeth and Merck are the only two U.S. manufacturers of that size that still use natural products as one of their sources to look for drugs," he said.

Newman's study found more than two-thirds of all drugs discovered in the last quarter-century have come from nature. He believes linking nature with advanced chemistry techniques that combine a vast array of molecules to speed drug development will likely yield much more fruitful results.

Newman and colleague Gordon Cragg reviewed the origins of new drugs developed in the past quarter-century and found that despite the introduction of a host of high-tech drug discovery tools, natural products continue to be the inspiration for most new drugs.

NATURAL INSPIRATION

Aspirin, a staple in most medicine cabinets, was originally obtained from the willow tree. The widely used chemotherapy treatment Taxol was derived from Pacific yew tree.

"Even though it is made in a different way now, it is absolutely identical to the material that comes from the yew," Newman said.

Likewise, the colon cancer treatment irinotecan, a standard chemotherapy that interferes with the growth of cancer cells, and topotecan, a chemotherapy used for ovarian cancer and lung cancer, are both modifications of the tree Camptotheca acuminata, a native of China.

In fact, Newman and Cragg found that about half of all anti-cancer drugs introduced since the 1940s are either natural products or medicines derived directly from natural products.

Newman's study, to be published in the March 23 issue of the Journal of Natural Products, is an expanded and updated version of reports published in 1997 and in 2003.

The researchers sought to trace how nature has inspired drugs currently on the market.

"A chemist would never conceive of making Taxol unless he or she had seen Taxol first," Newman said. "So what we looked back at was, what was the intellectual underpinning of the drugs that were currently on the market."

Newman said the advent of new drug discovery techniques such as combinatorial chemistry in the 1990s diverted many drug company resources away from a rich source of new drug compounds.

The technique allows for the rapid combination of many different but similar compounds -- basically industrializing the role of the chemist.

"Mother Nature's influence is alive and well," Newman said. "But you have to look for it in a subtle way. She doesn't come out and wave a broom in your face."